1. Field of the Invention
This invention relates to lightweight, portable, vibrating, concrete screeds.
2. Description of the Prior Art
Concrete floor or slab construction normally involves the steps of pouring, compacting, puddling, screeding, and surface finishing. Leveling of a concrete surface by hand with the aid of a straight edge supported on form boards and applied in a horizontal sawing motion is known to produce an extremely flat, smooth surface. However, the concrete in this practice is typically manually puddled or roughly smoothed by hoe-like boards before being smoothed by the straight edge. Thus, substantial manual labor is involved. Machines have been gradually developed to accomplish many of the conventional manual screeding steps. vibrating beams or screeds which compact and screed the concrete at the same time are generally used on concrete floor slabs. In order to achieve the necessary compaction effect, the beams are equipped with vibrators driven by electric motors or gasoline engines. These heavy machines are difficult to use and move from one location to another and are costly to acquire and maintain.
Several types of relatively lightweight and less expensive, vibrating concrete screeds have been produced. These vibrating concrete screeds utilize different types of vibrating devices which are usually spaced along the length of the screed. However, the main force of vibration is not uniformly spread along the length of the screed because of being concentrated near the vibrating unit. Vibration imparted to the concrete by screeds of this type often have a tendency to be damped out completely or to be drastically reduced at the extremities of the screed supported on the concrete form. With the foregoing in mind, applicant has heretofore provided an improved, lightweight and portable concrete screed having two vibrated blades and which is fully described in applicant's prior U.S. Pat. No. 4,030,873. While providing significant improvement over the prior art screeding devices, the vibrating concrete screed described in U.S. Pat. No. 4,030,873 has also been found to be in need of improvement. In particular, substantial manual puddling has still been required even with the improved apparatus described in applicant's patent. Difficulty has been encountered in the screeding process when the rough concrete in front of the screed is very irregular, i.e., where there are mounds and valleys of concrete to be finished. It has also been found that the concrete will sometimes run under the leading vibrating blade when the screed is pulled forward through the concrete as the blades are vibrated. Also, it would be desirable to reduce the amount of force required to advance the screed forwardly so as to reduce the force needed for winching or manual pulling of the screed.
It, thus, becomes the general purpose of the present invention to improve upon the vibrating concrete screed described in applicant's U.S. Pat. No. 4,030,873.